x86/hvm: Fix UB on defensive default case in handle_pio()

There's a potential 32bit left-shift (when size is 4) to a 32bit value,
which would trigger UB and tickle UBSAN the wrong way. Shifting right an
all-ones mask fixes the issue.

Fixes: 4609fc8eb0 ("x86/hvm: Improve error information in handle_pio()")
Signed-off-by: Alejandro Vallejo <alejandro.garciavallejo@amd.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/hvm/io.c

@@ -135,7 +135,7 @@ bool handle_pio(uint16_t port, unsigned int size, int dir)
     default:
         gprintk(XENLOG_ERR, "Unexpected PIO status %d, port %#x %s 0x%0*x\n",
                 rc, port, dir == IOREQ_WRITE ? "write" : "read",
-                size * 2, data & ((1u << (size * 8)) - 1));
+                size * 2, data & (UINT32_MAX >> (32 - size * 8)));
         domain_crash(curr->domain);
         return false;
     }